In many radio communication systems, a subscriber unit is provided with features for initiating calls to a target communicant. For example, a subscriber unit operating within a two-way dispatch radio system may offer various operation modes, including a dispatch or instant conferencing mode, and direct call modes, such as telephone interconnect and private call. In dispatch mode, a call is transmitted on an open communication channel, which may be selected at the subscriber unit, or provided by the system. In direct call mode, a call is initiated using a communication target identifier, such as a call number. Thus, a direct call generally requires prior availability of a target unit identifier. This target unit identifier may be known by the user, or may be stored in a preprogrammed list at the subscriber unit. A problem occurs when the target unit identifier is unknown or has changed. The user may then require assistance in obtaining the correct target unit identifier.
Telephone systems offering directory assistance are known. For example, U.S. Pat. No. 5,339,352, issued to Armstrong, et al. on Aug. 16, 1994, describes Directory Assistance Call Completion Via Mobile Systems. Here, a cellular radio system interfaces with an operating service system to obtain telephone number information from an identified directory listing. Such systems, while providing a useful service, require human interaction and are expensive to operate.
It is desirable to provide for the placement of calls from a subscriber unit operating within a radio communication system, when a target unit identifier is not locally available. Therefore, a new method of placing a call in a radio communication system is needed.